The invention relies in the field of recovering cold at very low temperature, the source of cold being liquid methane under pressure, e.g. obtained when transferring liquefied natural gas from methane tankers.
It should be recalled that methane is usually transported in a tanker at atmospheric pressure, with heat losses being compensated by the methane boiling at atmospheric pressure.
When the tanker reaches its unloading port, the methane is extracted by pumps that compress the liquid methane to a typical pressure of 6 megapascals (MPa).
This liquid phase compression consumes about one-thirtieth of the energy that would be required for compressing the gas phase and it is needed in order to distribute the natural gas in the primary network; it serves to compensate for the head losses associated with the flow of gas over several hundreds of kilometers.
In practice, liquefied methane is transferred under pressure to the distribution network after being heated up to a temperature of about 15° C. in heat exchangers that are immersed in the sea.
The recoverable cold power amounts to tens of megawatts.
At present very little use is made of that cold.
In a preferred but non-limiting embodiment, the invention proposes using the cold recovered from methane to capture the CO2 contained in flue gas, or more generally in any gas, by frosting.
The person skilled in the art will understand that this use imposes a particular constraint, given that the flow rates of the methane and of the gas conveying CO2 are independent.
The invention thus seeks to provide a system for recovering cold from methane obtained by liquid phase compression and suitable for use in capturing CO2 by frosting, in which the flow rate of methane and of the CO2-conveying gas are considered as being completely uncorrelated.
Documents US 2007/0186563 and WO 02/060561 respectively describe a method of recovering cold from methane, and a refrigeration method for capturing CO2 from the flue gases of energy production units.